This application makes reference to, incorporates the same herein, and claims all benefits according under 35 U.S.C. xc2xa7119 from an application for MICROWAVE OVEN AND CONTROL METHOD THEREOF earlier filed in the Korean Industrial Property Office on the Jul. 27, 2000 and there duly assigned Serial No. 43478/2000.
1. Field of the Invention
The present invention relates in general to a microwave oven and a method for controlling the same, and more particularly, to a microwave oven and a method for controlling the same, capable of stabilizing a circuit system therein by controlling a conversion control signal.
2. Description of the Related Art
FIG. 6 is a circuit diagram schematically showing a figuration of a conventional microwave oven. As shown therein, the conventional microwave oven is comprised of a power supply part 51, a high voltage transformer 53 generating a high voltage by means of the power supplied from the power supply part 51, a magnetron 55 generating electromagnetic waves by means of the high voltage generated by the high voltage transformer 53 to heat food within a cooking compartment of the microwave oven, a relay switch 57 switching on and off the supply of the power and a frequency, and a control part 59 controlling the high voltage transformer 53, the magnetron 55 and the relay switch 57 when the power is supplied from the power supply part 51.
With this configuration, if the power is supplied from the power supply part 51 and the relay switch 57 turns on by means of control of the control part 59, an electric current starts to flow at the primary winding of the high voltage transfer, thereby generating a high voltage at the secondary winding of the high voltage transformer 53. In the secondary winding of the high voltage transformer 53 are provided a voltage having a few volts to heat filaments of the magnetron 55 and a voltage of thousands volts to oscillate the magnetron 55. In order to apply a direct current to a negative pole of the magnetron 55, a rectifying and filtering means for rectifying and filtering the electric current is also provided therein.
However, since the core of the high voltage transformer 53 used in the conventional microwave oven is made of a silicon steel sheet, it is heavy and bulky, and it is inconvenient for consumers to handle it. Because the number of turns for the secondary winding of the high voltage transformer should increase in order to generate a high voltage from the high voltage transformer 53, this causes a problem that the high voltage transformer 53 must further increases in dimension.
In addition, to adjust an output voltage from the secondary winding of the high voltage transformer, the conventional microwave oven employs a method of controlling a duty cycle, because it is not possible to perform an analog control from a low output to a high output. The duty cycle control method controls the maximum rated output supplied from the power supply part 51 with a ratio of an on time and an off time of the high voltage transformer. In the duty cycle control method, if the on-time of the maximum rated output is short and the off-time thereof is long, the low output is generated, whereas the high output is generated if the on-time of the maximum rated output is long and the off-time thereof is short. Where the output is adjusted by the duty cycle control method, there is a great variation in temperature affecting cooking of food, which may lower an efficiency in cooking and further cause the food to be ill-tasting.
Accordingly, the present invention has been made in view of the above-described shortcomings, and it is an object of the present invention to provide a microwave oven able to facilitate an output control by allowing a high voltage transformer to continuously and variably generate a high voltage output from the secondary winding thereof in an analog form.
This and other objects of the present invention may be achieved by a provision of a microwave oven, comprising a microwave oven comprising a power supply part supplying a commercial alternating current (AC) power, a rectifying and filtering part rectifying and filtering the commercial AC power, a high voltage transformer generating a high voltage by means of direct s current (DC) power from the rectifying and filtering part; and a magnetron generating electromagnetic waves based on the high voltage from the high voltage transformer, further comprising a control signal generator part generating a control signal; an inverter part converting the DC power from the rectifying and filtering part into a high voltage AC power based on the control signal from the control signal generator part, and a control part blocking the control signal converted through the inverter part from being applied to the magnetron if the converted control signal is not within a predetermined range.
The control part includes a D/A converter part converting the control signal from the control signal generator part into an analog signal, a detector part detecting whether the control signal converted by the D/A converter part is within the predetermined range, an output control part controlling an output of the control signal passing through the detector part, and an oscillator part varying the control signal outputted by the output control part and inputting the varied control signal into the inverter part.
The control part further includes an on-off and soft starter part controlling an on-off operation and a soft start operation of the oscillator part depending upon the control signal.
The control part further includes a low voltage off part supplying a stop signal to the on-off and soft starter part and the D/A converter part where an abnormal power is inputted through the power supply part, to stop an operation of the on-off and soft starter part and the D/A converter part.
The control signal detected by the detector part is applied to an input terminal of the output control part.
The output control part uses a resistance property between a drain and a source of a field effect transistor (FET).
The oscillator part includes a switching part switching the DC power into an AC power.
An oscillating frequency of the oscillator part is given an expression Fo=1/(1.4xc3x97(external resistance+75)xc3x97capacitor).
The on-off and soft starter part uses a resistance property between a drain and a source of an FET.
The low voltage off part includes a transistor and a photo coupler which are connected in series to each other, to form a logical product (AND) circuit element.
The high voltage transformer includes a ferrite core to minimize a loss in a high frequency. frequency.
A method controlling a microwave oven including a power supply part supplying a commercial alternating current (AC) power, a rectifying and filtering part rectifying and filtering the commercial AC power, an inverter part converting a DC power from said rectifying and filtering part into an AC power of a high frequency, a high voltage transformer generating a high voltage by means of the AC power from the inverter part, and a magnetron generating electromagnetic waves based on the high voltage from the high voltage transformer, includes the steps of generating a control signal, applying the control signal to the inverter part so that the inverter part converts the DC power from the rectifying and filtering part into the high frequency AC power, detecting whether the control signal converted through the inverter part is within a predetermined range, and preventing the control signal from being applied to the magnetron if the control signal is not within the predetermined range.
The method further includes the steps of determining whether the control signal to be applied to the inverter part is within the predetermined range and preventing the control signal from entering into the inverter part if the control signal is not within the predetermined range.